Using
an ordinary phone for most people is a common daily occurrence as is listening
to your favorite CD containing the digitally recorded music. It is only a small
extension to these technologies in having your voice transmitted in data packets.
The transmission of voice in the phone network was done originally using an analog
signal but this has been replaced in much of the world by digital networks. Although
many of our phones are still analog, the network that carries that voice has become
digital.In todays phone networks,
the analog voice going into our analog phones is digitized as it enters the phone
network. This digitization process, shown in Figure 1 below, records a sample
of the loudness (voltage) of the signal at fixed intervals of time. These digital
voice samples travel through the network one byte at a time.At the destination
phone line, the byte is put into a device that takes the voltage number and produces
that voltage for the destination phone. Since the output signal is the same as
the input signal, we can understand what was originally spoken.The evolution of
that technology is to take numbers that represent the voltage and group them together
in a data packet similar to the way computers send and receive information to
the Internet.

Voice over IP is the technology of taking units of sampled speech
data .So at its most basic level, the concept of VoIP is straightforward. The
complexity of VoIP comes in the many ways to represent the data, setting up the
connection between the initiator of the call and the receiver of the call, and
the types of networks that carry the call.Using
data packets to carry voice is not just done using IP packets. Although it won't
be discussed, there is also voice over Frame Relay (VoFR) and Voice over ATM (VoATM)
technologies. Many of the issues VoIP being discussed also apply to the other
packetized voice technologies.The increasing multimedia contents in Internet have
reduced drastically the objections to putting voice on data networks.